The preferred embodiment concerns a method and a device for processing a measurement signal to detect a property of a toner mark, in which method the toner mark is generated with the aid of an image generation device. The toner mark is detected with the aid of a measurement arrangement in that the measurement arrangement outputs determined sample values as a measurement signal at sample points in time.
In electrographic high-capacity printers for printing of single sheets or web-shaped substrate material with printing capacities of >50 pages DIN A4/minute, up to a few 100 sheets of DIN A4/minute, as well as print and image generation speeds of up to 2 m/sec at present, large quantities of toner material can be consumed within a relatively short time to generate the print images. In such electrographic high-capacity printers, inking rules are used in order to keep the degree of inking of print images constant. Electrographic image generation methods comprise, for example, electrographic, magnetographic and ionographic image generation methods.
A method and a device to control a printing process are known from the document DE 101 36 259 A1 and the parallel U.S. Pat. No. 7,016,620 B2, in which printing process a toner mark is generated on an intermediate carrier by a character generator with a lower energy than the energy applied to generate other print images, such that the color density of the inked toner mark is reduced. A reflection sensor determines the color density of the inked toner mark, wherein the toner concentration in a developer station is set depending on the determined color density.
Measurement arrangements to determine the layer thickness of a toner mark with the aid of capacitive sensors are also known from the document DE 101 51 703 A1 and the parallel U.S. Pat. No. 6,771,913 B2. The cited documents are herewith incorporated by reference into the present Specification.
In order to improve the half-tone reproduction as well as the quality of multicolor printing, in which multiple color separations of different colors are printed atop one another, it is necessary to also detect small toner quantities (in particular of toner marks that are not inked over the entire area). The actual printed density or the average layer thickness of the toner mark is advantageously already measured at the photoconductor with the aid of a measurement device and thus is immediately measured after the development of a latent print image into a toner image. The optical density of a full-tone mark and/or the point size of raster points inked with toner can be regulated with the aid of the measurement result. Given use of a capacitive sensor to determine the layer thickness of the toner particle layer of the toner mark, the dielectricity or relative permittivity of the toner with whose toner particles the toner mark is inked is that quantity on which the measurement method is based.
In addition to toners with the standard colors cyan (C), magenta (M), yellow (Y) and black (K), special colors (in particular also customer-specific special colors) can be used in high-capacity printers, which special colors exhibit a dielectricity deviating from that of standard colors depending on the material composition. In particular given low dielectricities and/or small toner quantities of the toner mark to be detected by a capacitive sensor, only capacity changes in the femtofarad range can be determined by a capacitive sensor, whereby only low signal strengths are output to the capacitive sensor. Very slight perturbations can thereby severely distort the measurement result. An inking and/or point size regulation that is required for the image generation process can thereby be severely plagued with errors, whereby the quality of the image generation process can no longer be ensured.